Continuing a loop until good input?

I'm trying to make a program where the user needs an account to access other parts of it. I want this set up so that if the user's 2 confirm password dont match, they have to reenter the info. Also, if the user leaves anything blank, they must reenter all the info. How can I do this so it continues to loop until the user enters good info?

if (e.getSource() == okButton) {
        if(!passString.equals(passStringConfirm) || userName.equals(null) || passString.equals(null) || passStringConfirm.equals(null)){
                enterUsername.setText("");
                enterPassword.setText("");
                enterConfirmPassword.setText("");
                }
            }

This is what I have so far, and if only works for one iteration. I tried do while and it would continually print out the warning message I was trying to print out in a JOptionPane.

import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPasswordField;
import javax.swing.JTextField;
import javax.swing.border.Border;

public class CreateAccount extends JFrame implements ActionListener {

    JLabel username = new JLabel("Enter your username");
    JTextField enterUsername = new JTextField(null, 15);
    JLabel password = new JLabel("Enter your password");
    JPasswordField enterPassword = new JPasswordField(null, 15);
    JLabel passwordConfirm = new JLabel("Confirm your password.");
    JPasswordField enterConfirmPassword = new JPasswordField(null, 15);
    JButton okButton = new JButton("OK");

    String userName;
    double initialDeposit;

    public CreateAccount() {

        add(username);
        add(enterUsername);
        add(password);
        add(enterPassword);
        add(passwordConfirm);
        add(enterConfirmPassword);
        add(okButton);

        okButton.addActionListener(this);

        setTitle("New Bank Account Creation");
        setVisible(true);
        setLocationRelativeTo(null);
        setSize(270, 300);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLayout(new FlowLayout());

    }

    @Override
    public void actionPerformed(ActionEvent e) {

        char[] pass = enterPassword.getPassword();
        String passString = new String(pass);
        char[] passConfirm = enterConfirmPassword.getPassword();
        String passStringConfirm = new String(passConfirm);

        userName = enterUsername.getText();

        if (e.getSource() == okButton) {
            if(userName == null || userName.isEmpty() || passString == null || passString.isEmpty() || !passString.equals(passStringConfirm)) {
                    enterUsername.setText("");
                    enterPassword.setText("");
                    enterConfirmPassword.setText("");
                    Border redLine = BorderFactory.createLineBorder(Color.red);
                    enterUsername.setBorder(redLine);
                    enterPassword.setBorder(redLine);
                    enterConfirmPassword.setBorder(redLine);
                    repaint();
                    }
                }
            super.dispose();

            int response = 0;
            String firstDesposit = JOptionPane.showInputDialog("Welcome " + userName + ". Enter your initial deposit.");
            initialDeposit = Double.parseDouble(firstDesposit);
            if (response == JOptionPane.OK_OPTION) {
                new Menu();
            }
        }
    }

Your if test cannot be correct. If any of your String(s) are null you would get a NullPointerException. I think you wanted

if (userName == null || userName.isEmpty() || passString == null
            || passString.isEmpty()
            || !passString.equals(passStringConfirm)) {
    enterUsername.setText("");
    enterPassword.setText("");
    enterConfirmPassword.setText("");
}

Then your UI code should check if those are empty before allowing the user to proceed. Finally, in the code above I believe you might use setBorder() to give those fields a red border.

if (userName == null || userName.isEmpty() || passString == null
            || passString.isEmpty()
            || !passString.equals(passStringConfirm)) {
    Border redLine = BorderFactory.createLineBorder(Color.red);
    enterUsername.setText("");
    enterPassword.setText("");
    enterConfirmPassword.setText("");
    enterUsername.setBorder(redLine);
    enterPassword.setBorder(redLine);
    enterConfirmPassword.setBorder(redLine);
}

Edit

Based on the code you provided, but you need it in an else!

if(userName == null || userName.isEmpty() || passString == null
        || passString.isEmpty() || !passString.equals(passStringConfirm)) {
    enterUsername.setText("");
    enterPassword.setText("");
    enterConfirmPassword.setText("");
    Border redLine = BorderFactory.createLineBorder(Color.red);
    enterUsername.setBorder(redLine);
    enterPassword.setBorder(redLine);
    enterConfirmPassword.setBorder(redLine);
    repaint();
} else { // <-- add this
    super.dispose();
    int response = 0;
    String firstDesposit = JOptionPane.showInputDialog(
            "Welcome " + userName + ". Enter your initial deposit.");
    initialDeposit = Double.parseDouble(firstDesposit);
    if (response == JOptionPane.OK_OPTION) {
        new Menu();
    }
}